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5 Trend functions

Trend functions, in contrast to history functions, use trend data for calculations.

Trends store hourly aggregate values. Trend functions use these hourly averages, and thus are useful for long-term analysis.

Trend function results are cached so multiple calls to the same function with the same parameters fetch info from the database only once. The trend function cache is controlled by the TrendCacheSize server parameter.

Triggers that reference trend functions only are evaluated once per the smallest time period in the expression. For instance, a trigger like

trendavg(/host/key,1d:now/d) > 1 or trendavg(/host/key2,1w:now/w) > 2

will be evaluated once per day. If the trigger contains both trend and history (or time-based) functions, it is calculated in accordance with the usual principles.

All functions listed here are supported in:

Some general notes on function parameters:

  • Function parameters are separated by a comma
  • Optional function parameters (or parameter parts) are indicated by < >
  • Function-specific parameters are described with each function
  • /host/key and time period:time shift parameters must never be quoted
Common parameters
  • /host/key is a common mandatory first parameter
  • time period:time shift is a common second parameter, where:
    • time period - the time period (minimum '1h'), defined as <N><time unit> where N - the number of time units, time unit - h (hour), d (day), w (week), M (month) or y (year).
    • time shift - the time period offset (see function examples)

Trend functions

FUNCTION
Description Function-specific parameters Comments
baselinedev (/host/key,data period:time shift,season_unit,num_seasons)
Returns the number of deviations (by stddevpop algorithm) between the last data period and the same data periods in preceding seasons. data period - the data gathering period within a season, defined as <N><time unit> where
N - number of time units
time unit - h (hour), d (day), w (week), M (month) or y (year), must be equal to or less than season

Time shift - the time period offset (see examples)

season_unit - duration of one season (h, d, w, M, y), cannot be smaller than data period

num_seasons - number of seasons to evaluate
Examples:
=> baselinedev(/host/key,1d:now/d,"M",6) → calculating the number of standard deviations (population) between the previous day and the same day in the previous 6 months. If the date doesn't exist in a previous month, the last day of the month will be used (Jul,31 will be analysed against Jan,31, Feb, 28,... June, 30).
=> baselinedev(/host/key,1h:now/h,"d",10) → calculating the number of standard deviations (population) between the previous hour and the same hours over the period of ten days before yesterday.
baselinewma (/host/key,data period:time shift,season_unit,num_seasons)
Calculates the baseline by averaging data from the same timeframe in multiple equal time periods ('seasons') using the weighted moving average algorithm. data period - the data gathering period within a season, defined as <N><time unit> where
N - number of time units
time unit - h (hour), d (day), w (week), M (month) or y (year), must be equal to or less than season

Time shift - the time period offset, defines the end of data gathering time frame in seasons (see examples)

season_unit - duration of one season (h, d, w, M, y), cannot be smaller than data period

num_seasons - number of seasons to evaluate
Examples:
=> baselinewma(/host/key,1h:now/h,"d",3) → calculating baseline based on the last full hour within a 3-day period that ended yesterday. If "now" is Monday 13:30, the data for 12:00-12:59 on Friday, Saturday, and Sunday will be analyzed.
=> baselinemwa(/host/key,2h:now/h,"d",3) → calculating baseline based on the last two hours within a 3-day period that ended yesterday. If "now" is Monday 13:30, the data for 10:00-11:59 on Friday, Saturday, and Sunday will be analyzed.
=> baselinewma(/host/key,1d:now/d,"M",4) → calculating baseline based on the last days of previous 4 months, excluding the last full month. If today is September 1st, the data for July 31st, June 30th, May 31st, April 30th will be analyzed.
trendavg (/host/key,time period:time shift)
Average of trend values within the defined time period. See common parameters. Examples:
=> trendavg(/host/key,1h:now/h) → average for the previous hour (e.g. 12:00-13:00)
=> trendavg(/host/key,1h:now/h-1h) → average for two hours ago (11:00-12:00)
=> trendavg(/host/key,1h:now/h-2h) → average for three hours ago (10:00-11:00)
=> trendavg(/host/key,1M:now/M-1y) → average for the previous month a year ago
trendcount (/host/key,time period:time shift)
Number of successfully retrieved trend values within the defined time period. See common parameters. Examples:
=> trendcount(/host/key,1h:now/h) → count for the previous hour (e.g. 12:00-13:00)
=> trendcount(/host/key,1h:now/h-1h) → count for two hours ago (11:00-12:00)
=> trendcount(/host/key,1h:now/h-2h) → count for three hours ago (10:00-11:00)
=> trendcount(/host/key,1M:now/M-1y) → count for the previous month a year ago
trendmax (/host/key,time period:time shift)
The maximum in trend values within the defined time period. See common parameters. Examples:
=> trendmax(/host/key,1h:now/h) → maximum for the previous hour (e.g. 12:00-13:00)
=> trendmax(/host/key,1h:now/h) - trendmin(/host/key,1h:now/h) → calculate the difference between the maximum and minimum values (trend delta) for the previous hour (12:00-13:00)
=> trendmax(/host/key,1h:now/h-1h) → maximum for two hours ago (11:00-12:00)
=> trendmax(/host/key,1h:now/h-2h) → maximum for three hours ago (10:00-11:00)
=> trendmax(/host/key,1M:now/M-1y) → maximum for the previous month a year ago
trendmin (/host/key,time period:time shift)
The minimum in trend values within the defined time period. See common parameters. Examples:
=> trendmin(/host/key,1h:now/h) → minimum for the previous hour (e.g. 12:00-13:00)
=> trendmin(/host/key,1h:now/h) - trendmin(/host/key,1h:now/h) → calculate the difference between the maximum and minimum values (trend delta) for the previous hour (12:00-13:00)
=> trendmin(/host/key,1h:now/h-1h) → minimum for two hours ago (11:00-12:00)
=> trendmin(/host/key,1h:now/h-2h) → minimum for three hours ago (10:00-11:00)
=> trendmin(/host/key,1M:now/M-1y) → minimum for the previous month a year ago
trendstl (/host/key,eval period:time shift,detection period,season,<deviations>,<devalg>,<s_window>)
Returns the rate of anomalies during the detection period - a decimal value between 0 and 1 that is ((the number of anomaly values)/(total number of values)). eval period - the time period that must be decomposed (minimum '1h'), defined as <N><time unit> where
N - number of time units
time unit - h (hour), d (day), w (week), M (month) or y (year).

Time shift - the time period offset (see examples)

detection period - the time period before the end of eval period for which anomalies are calculated (minimum '1h', cannot be longer than eval period), defined as <N><time unit> where
N - number of time units
time unit - h (hour), d (day), w (week).

season - the shortest time period where a repeating pattern ("season") is expected (minimum '2h', cannot be longer than eval period, number of entries in the eval period must be greater than the two times of the resulting frequency (season/h)), defined as <N><time unit> where
N - number of time units
time unit - h (hour), d (day), w (week).

deviations - the number of deviations (calculated by devalg) to count as anomaly (can be decimal), (must be greater than or equal to 1, default is 3)

devalg (must be double-quoted) - deviation algorithm, can be stddevpop, stddevsamp or mad (default)

s_window - the span (in lags) of the loess window for seasonal extraction (default is 10 * number of entries in eval period + 1)
Examples:
=> trendstl(/host/key,100h:now/h,10h,2h) → analyse the last 100 hours of trend data,
find the anomaly rate for the last 10 hours of that period,
expecting the periodicity to be 2h,
the remainder series values of the evaluation period are considered anomalies if they reach the value of 3 deviations of the MAD of that remainder series
=> trendstl(/host/key,100h:now/h-10h,100h,2h,2.1,"mad") → analyse the period of 100 hours of trend data, up to 10 hours ago,
find the anomaly rate for that entire period
expecting the periodicity to be 2h,
the remainder series values of the evaluation period are considered anomalies if they reach the value of 2,1 deviations of the MAD of that remainder series
=> trendstl(/host/key,100d:now/d-1d,10d,1d,4,,10) → analyse 100 days of trend data up to a day ago,
find the anomaly rate for the period of last 10d of that period,
expecting the periodicity to be 1d,
the remainder series values of the evaluation period are considered anomalies if they reach the value of 4 deviations of the MAD of that remainder series,
overriding the default span of the loess window for seasonal extraction of "10 * number of entries in eval period + 1" with the span of 10 lags
=> trendstl(/host/key,1M:now/M-1y,1d,2h,,"stddevsamp") → analyse the previous month a year ago,
find the anomaly rate of the last day of that period
expecting the periodicity to be 2h,
the remainder series values of the evaluation period are considered anomalies if they reach the value of 3 deviation of the sample standard deviation of that remainder series
trendsum (/host/key,time period:time shift)
Sum of trend values within the defined time period. See common parameters. Examples:
=> trendsum(/host/key,1h:now/h) → sum for the previous hour (e.g. 12:00-13:00)
=> trendsum(/host/key,1h:now/h-1h) → sum for two hours ago (11:00-12:00)
=> trendsum(/host/key,1h:now/h-2h) → sum for three hours ago (10:00-11:00)
=> trendsum(/host/key,1M:now/M-1y) → sum for the previous month a year ago